# CVE-2026-55636: Capsule: Incomplete fix of CVE-2026-30963: singular/plural typo leaves namespaces/finalize unprotected

> Attackers with specific RBAC permissions can bypass validation to modify namespace tenant labels due to a typo in webhook configuration.

- **Severity:** Medium 5.7 (`CVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:U/C:L/I:H/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** An administrator
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 15 Sep 2026
- **Updated:** 15 Sep 2026
- **Also known as:** GHSA-gwxr-7h77-7777, GO-2026-5406

## What is CVE-2026-55636?

CVE-2026-55636 is a medium-severity missing authorization vulnerability in projectcapsule capsule, published on 15 Sep 2026. An attacker needs administrator access to exploit it, and only if a user opens a file or follows a link.

### Official description

Capsule is a multi-tenancy and policy-based framework for Kubernetes. From 0.13.0 until 0.13.6, charts/capsule/templates/configuration.yaml configures the validating webhook with namespace/finalize instead of the Kubernetes resource name namespaces/finalize. A user with namespaces/finalize RBAC can send a PUT request to /api/v1/namespaces/{namespace}/finalize, and the singular rule never matches the plural resource, so the validating webhook is not invoked and the user can change the namespace tenant label. matchPolicy: Equivalent does not compensate because it handles API group and version equivalence rather than resource-name errors. This vulnerability is fixed in 0.13.6.

Weakness: CWE-863 (Incorrect Authorization)

## Which versions are affected by CVE-2026-55636?

3 open source packages ship an affected version, including github.com/projectcapsule/capsule.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `github.com/projectcapsule/capsule` | Go | From 0.13.0 | 0.13.6 |
| `github.com/projectcapsule/capsule` | Go | From 0.13.0 | 0.13.6 |
| `github.com/projectcapsule/capsule` | Go | From 0.13.0 | 0.13.6 |

## How do I fix CVE-2026-55636?

Upgrade github.com/projectcapsule/capsule to 0.13.6 or later.

## Is CVE-2026-55636 being exploited?

There is no known exploitation of CVE-2026-55636 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-55636 and fix it if it is affected.

What it is: CVE-2026-55636 is a medium-severity missing authorization vulnerability in projectcapsule capsule, published on 15 Sep 2026. An attacker needs administrator access to exploit it, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-55636 in the wild and no public exploit code.

Affected packages and fixed versions:
- github.com/projectcapsule/capsule (Go): affected from 0.13.0; fixed in 0.13.6
- github.com/projectcapsule/capsule (Go): affected from 0.13.0; fixed in 0.13.6
- github.com/projectcapsule/capsule (Go): affected from 0.13.0; fixed in 0.13.6

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-55636/ (Markdown: https://insights.sbomify.com/CVE-2026-55636/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-55636
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-55636
- OSV: https://osv.dev/vulnerability/CVE-2026-55636

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-55636/
Summaries are generated and may contain mistakes; the official description above is the record.